Uncovering the Influence of Ni²⁺ Doping in Lead-Halide Perovskite Nanocrystals Using Optically Detected Magnetic Resonance Spectroscopy

Abstract

Magnetic doping in halide perovskite semiconductors is of timely interest in the pursuit of new optical and magnetic properties that surpass those of the existing undoped materials. Here, we report a thorough investigation of the optical and magneto-optical properties of Ni 2+ -doped cesium lead halide perovskite with a chemical formula CsPb(Br 1−x Cl x ) 3 , implementing steady-state and transient photoluminescence (PL), polarized magneto-PL, and optically detected magnetic resonance (ODMR) spectroscopies. The magneto-PL measurements revealed three PL features with different degrees of circular polarization, associated with recombination from band-edge and trapping states. The ODMR measurements probed magnetic resonance transitions of photogenerated electrons and holes with phenomenological g-factors that deviate from those of band-edge states. Simulations of the ODMR spectra suggested carriers' trapping in shallow traps with a slight anisotropic surrounding and with weak electron−hole exchange coupling. Furthermore, we observed substantial broadening of the hole resonance, due to its spin-exchange coupling with the Ni 2+ unpaired spins. Overall, these ODMR measurements uncovered the role of the dopant in localizing photogenerated carriers by stiffening (becoming more rigid by decreasing the structural dynamics) the crystal structure and, for the first time, provide a direct observation of carrier-dopant spin exchange interactions in metal-halide perovskite nanocrystals. These results offer insight into the influence of magnetic dopants on the electronic structures of metal-halide perovskites, with a view toward emerging spin-based devices made from perovskites.

Luminescence Enhancement Due to Symmetry Breaking in Doped Halide Perovskite Nanocrystals

“…We therefore also exclude any significant doping-induced influence on the spin dynamics of the perovskite with respect to the optoelectronic properties at room temperature and for our studied NC sizes, leaving the discussed charge localization effects as the only relevant ones that intrinsically impact the light emission under device-relevant conditions. While a recent report on the influence of nickel doping suggests a certain degree of spin-exchange coupling, 29 those measurements relied on the presence of strong magnetic fields and low temperatures, making the phenomena conceptually interesting for spintronics applications but unlikely to impact the optoelectronic properties under device conditions, that is, at room temperature and zero field. We can thus now conclude with the following remarks for the informed choice of the dopant system.…”

Submillisecond Spin Relaxation in CsPb(Cl,Br)3 Perovskite Nanocrystals in a Glass Matrix

“…Very recently, long longitudinal spin relaxation times of 0.2 ms for electrons and 0.78 ms for holes have been measured at T = 4 K using ODMR in Ni 2+ -doped CsPb­(Cl,Br) 3 NCs . At the same time, no ODMR signal has been detected for undoped reference NCs.…”

Understanding Antiferromagnetic Coupling in Lead-Free Halide Double Perovskite Semiconductors

“…A lead-halide perovskite is typically nonmagnetic, but the structural and chemical diversity of the MHPs allow the incorporation of magnetic ions that lead to magnetic response and the modification of the optical properties of nonmagnetic MHPs. , More importantly, a structural derivative such as cesium halide double perovskites with a general formula of A 2 B I B III X 6 , where A is Cs 1+ cations, B I are monovalence metal cations (+1), B III are trivalence metal cations (+3), and X are halide anions, e.g., Cl 1– , Br 1– , I 1– , allows the search for new magnetic alloys by incorporating transition/rare-earth metal ions at the B III site. Very recently, nontoxic and stable Cs 2 (Ag:Na)­FeCl 6 semiconductor alloys have been synthesized, demonstrating a rich functionality.…”